Method of making dynamic speakers



Nov. 5, 1 935. J. P. QUAM V 2,020,212

METHODOF MAKING DYNAMIC SPEAKERS Filed Sept. 6, 1935 2 sheets sheet 1 I 7271/57 UT."

Jamgs .Q'zzam.

NOV. 5, 1935- 1 QUAM 2,020,212

METHOD OF MAKING DYNAMIC SPEAKERS Filed Sept. 6, 1935 2 Sheets-Sheet 2 JHUET'FET 22755 471/5172.

Patented Nov. 5, 1935 UNITED STATES PATENT OFFICE 2,020,212 METHOD OF MAKING DYNAMIC SPEAKERS James P. Quam, Chicago, Ill. Application September a, 1925, Serial No. 39,459

12 Claims.

This invention relates to loud speakers and more particularly to the method of making dynamic speakers of the type ordinarily employed with radio receiving sets. Dynamic speakers are those in which the cone or other diaphragm generating the sound waves is actuated by a small coil, called thevoice coll, which operates in an intense magnetic field in an annular gap formed around one end of the core of an electro-magnet by the magnetic yoke of the magnet. The voice coil carries the telephonic current which is translated into sound.

The present application is a continuation in part of my three co-pending prior applications having Serial Numbers 670,865, 723,034 and 750,429, filed respectively May 13, 1933, April 28, 1934, and October 29, 1934. It is the purpose of the present application to cover certain important features disclosed in but not patented by said prior applications, and in this connection to disclose these features in the combination in which they are most advantageous.

In this form of the invention now considered most advantageous the voice coil is secured directly to the cone and the cone is supported by a frame welded to the yoke of the field magnet to insure accurate alignment, and a flexible spider is secured to said frame guiding the voice coil in its movement. The formation of the field electro-magnet is an important feature, the yoke being formed without joints by bending a flat bar to a U-shape, and the core being driven into a hole in one leg of the U while being guided with respect to the voice coil hole in the other leg. This insures accuracy of centering of the core in the voice coil hole irrespective of parallelism of the legs of the yoke. The annular voice coil gap may be very narrow, since very little tolerance is necessary to allow for errors either in the centering of the core or the alignment of the voice coil.

The joint-free yoke, its intimate contact with the core, and the narrow voice coil gap all contribute to provide an extremely strong magnetic field in the gap. The strong field and the light cone and voice coil construction both contribute to provide exceptional volume of reproduction. This exceptional volume is obtained not at great cost but rather with great simplicity and much less cost.

It is apparent from the foregoing that one object of the invention is to provide a speaker of greater volume, with quality reproduction, and another object is to provide a speaker which can be made commercially at less cost. In the preferred form of the invention illustrated, both objects are attained.

For a better understanding of my invention, reference is made to the accompanying drawings, in which:

Fig. 1 is a side view of the preferred form of speaker.

Fig. 2 is a rear view of the same.

Fig. 3 is a sectional view taken substantially along the line 3-3 of Fig. 2. 10 Fig. 4 is a fragmentary detailed view showing the mounting of the voice coil on the cone.

Fig. 5 is a face view of the spider used for guiding the coil.

Fig. 6 is a fragmentary view illustrating a 13 slightly modified form of core structure.

Figs. '7 to 12 are diagrammatic illustrations of the method of forming the speaker.

Referring now more in'detail to the preferred form of construction illustrated, it will be seen 20 that the speaker includes a cone ll carried by a cone support I! and actuated by a voice coil l3 positioned in an annular gap ll of an electro-magne'tic field magnet.

Field magnet The preferred form of field magnet includes a U-shaped yoke or outer pole piece l8 and a core I! having one end driven into a hole IS in one leg of the yoke and having its other end centered in a hole l8 in the other leg of the yoke to form the annular gap ll. U-shaped permanent magnets have long been known, but prior to my invention the use of a simple U- shaped member as the yoke of an electro-magnet for dynamic speakers was not known. Perhaps it was assumed that to carry the flux of the field coil a cup-shaped member, or something similar to it and having magnetic paths on more than one side of the coil, was necessary. Or, perhaps, 40 any one who got beyond this assumption was blocked by the dimculty of centering the core in the voice coil hole in commercial practice when the legs of the U are likely not to be truly parallel. This difliculty is overcome by the present 45 invention. V

The yoke i8 is formed from a flat bar It of a suitable malleable iron capable of being spot welded. The hole l8 may first be punched in the flat bar, the punched bar being illustrated in Fig. 50 7. This punched bar is then bent to the U-shape shown in Fig. 8, this step preferably being performed by a suitable stamping press. Next,'the hole I9 is punched in alignment with the hole N. the punching plunger being guided thereby, 55

as diagrammatically illustrated in Fig. 0. Next, the holes It and II are line-reamed to insure their accurate alignment'and to bring them to the exactsisedesiredthereamingofhole Ilbeing diagrammatically illustrated by Fig. 10. At this stage the ears II of cone support I! are welded to the yoke, the resulting structure being illustrated in Fig. 11.

Next, a coil II, wound on a suitable spool or cover 22, and a closed ring 23 of a good conductor such as copper'are inserted between the legs of the yoke. Then the core I I is passed through the hole II and through the coil 2i and ring 23 and staked (driven) into the hole I I. The driving is preferably performed bya press plunger fl. While the core I1 is being driven into the hole IO, it is centered accurately in the hole II by means of a ring gauge 11, as'di'agrammatically illustrated in Fig. 12.

It might be assumed that the final position of core I! would be controlled entirely by the accuracy of alignment of holes II and II and that the ring gauge 21 would not be effective if there remained a slight inaccuracy of alignment, but apparently this is not the case, and even ifthe holes were accurately aligned this would not reliably prevent a slight eccentricity of the core II in hole II unless ring gauge 21 were used. However, since the hole II was substantially accurately aligned with the hole II, accurate centering of the core II with respect to the hole I8 is possible, and this result is in fact accomplished by the use of the ring gauge 21 during the insertion of the core. Even when the ring gauge 21 is removed, the core remains accurately centered in the hole IS. The dependability of this centering permits the use of a narrower air sap, since it is unnecessary to provide large tolerance to allow for inaccuracies of the centering of the core within the hole II.

Since the core I1 is secured in place by staking, this of course means that it should be slightly oversize with respect to the hole I I, so that when it is in place in said hole it will be in a state of elastic compression. This not only insures rigidity but also insures a'force-fit of intimate high pressure contact between the core I1 and the leg 20 of the yoke. The step of driving an oversize core into a hole inevitably scrapes the core and the wall of the hole clean, so that the joint is clean as well as under high pressure. This clean force-fit, togetherwith the fact that the gap I 4 is very small (much smaller than can be illustrated) and the remainder of the magnetic circuit is of one piece, results in a magnetic circuit of very high permeability. It followsthat with a given number of ampere turns in the coil II, the magnetic flux in the gap Il will be unusually strong. In this connection it should be noted that the yoke I. has a large cross-sectional area, the dimensions of the yoke and core being substantially as illustrated. It is desirable that this cross-sectional area of the yoke be at least as great as the cross-sectional area of the core I I. Contrary to what might have been supposed, this yoke can carry the magnetic field of the coil II, as commercially used, without undue loss of magnetic force due to reluctance. Apparently this is because the yoke is of such large cross section, both around the ends of the core and in the intermediate portion, that it does not come too close to the saturation point to be efficient.

In Fig. 6 is illustrated a slight modification of the invention in which the yoke I1 is provided aoaaaia with a reduced portion II of smaller diameter, so that an annular shoulder 32 is provided on the yoke. When the core I1 is driven into the leg II of the yoke, the annular shoulder 82 will seat on the leg 20'. The outer end of the stub 45 II mayormaynotbeupsetinthefiaredporticn 38 of the hole II.

If the inner face of leg I! and the shoul 82 both happen to be exactly perpendicular to the axis of the core II, as controlled by the ring 10 gauge 21, the leg 2! will contact the annular shoulder I! throughout its area. Since such absolute perfection is rarely obtained in commercial production, the engagement between the shoulder If and the leg'll' will usually be firm only at one point, although of course there may not be a visible air gap at any point. The provision of the shoulder 32 is therefore of doubtiul value, and in the preferred form of the invention, as shown in the other figures, the core I1 is of cylindrical'shape from end to end, except for a very slight rounding or beveling of its corners. If the ring gauge 21 were not used during the staking operation, the shoulder 32 would be harmful, since it would tend to tilt the g5 core out of its intended position whenever the leg I! was the least bit out of perpendicular to this intended position. The centering of the core independently of its being seated on the leg II or II, whether the shoulder 32 is provided )1 go not, may be referred to as free-centering".

Cone and voice coil mounting The cone I I is secured at its periphery to the cone support I 2 in any suitable manner, as by 35 being glued thereto. The cone support I2, which may be stamped from sheet metal, preferably non-magnetic includes the rim 4' and upper and lower brackets 41 extending therefrom, as shown, and terminating in the welding ears II. An outo wardly-extending ear 48 is formed on each of these brackets. A sheet may first be punched to form a fiat blank including the rim ll, brackets 41 and cars 20. Then this blank may be stamped to the shape shown. On each ear 4. is riveted a support stub 4|. On these stubs the spider I! is suspended, being secured in place by the nuts II. On one of the brackets ll there may also be secured a plate I! on which is mounted a transformer 53. go

The voice coil I3 is wound on the usual thin paper cylinder I which, according to the preferred form of this invention, is secured directly tothecone ll,asisillustratedbestinl"ig.4. The upper part of the cylinder II includes an outer layer 81 which .is glued or otherwise secured to a fiange 38 formed integrally on the cone II. The guide spider 3! is also secured to the cone II and the cylinder ii at this point, as

illustrated. The wire ll forming the voice coil is soldered to a terminal eyelet I! in the spider 3!, and therein is soldered to fiexible' lead II. Wire II passes inside the outer layer 31 of the cylinder 36 to the bottom thereof where it is wound around the inner layer of the cylinder 38 and extends back in the same manner to another terminal eyelet, shown only in Fig. 5.

The cone II may be made of the usual paper corrugated annularly to make it flexible and permit its vibrations. The spider 3! is of the usual 10 thin linen reinforced material stiff enough to act as a support or guide but permitting free vibration of the cone and voice coil when the spider arms are fastened at their ends. 'Because the ears 48 extend outwardly beyond the, edges of II,

the magnet yoke, and beyond the adjacent portions of the brackets 41, the spider 39 may be unusually long, thus permitting unusually free movement of the voice coil and cone, without danger of misalignment since the brackets H are welded in the proper positions. The spider is cut at an angle of 45 with the grain of the material for greater strength and to prevent warping. a

To insure permanent and accurate alignment of the cone II and the spider 39, and therefore the voice coil III, with respect to the voice coil gap M, the brackets 41 of the cone support I2 are spot welded to the yoke it, while the support is held exactly concentric with the hole I8 by a suitable jig.

Another simplified construction which I have provided is in the method of supporting the ends of the flexible conductors 6| of the voice coil. For this purpose I provide eyelets 62 passed through lower bracket 41 and insulatingly supported by this bracket through the use of a pair of insulating washers, as shown, one of which is secured against each face of the ear 28 and through which the eyelet 29 is passed, after which it is curled over. A voice coil conductor 6| is then passed into the eyelet 62 and soldered thereto, after which the corresponding conductor $3 from the transformer is soldered to the outside of the eyelet 62. Y

The combination of features Although each of the above described novel features is in itself useful in speakers not embodying the other features, it is when all of the features are combined that the best results are obtained. There is a chain of interrelations whereby each feature not only adds its own advantages but also enhances the advantages of the other features.

Thus the jointless yoke structure and its intimate joint with the core increase the magnetic potential at the gap, and it is increased still further on account of the reliable free-centering of the core in the pole which permits a reduction in the excess length of the gap provided for tolerance. This increased fiux is especially effective in view of the light weight of the moving parts resulting from mounting the voice coil directly on the cone. The mounting of the voice coil on the cone without increasing the width of the gap to accommodate variations and without adjustments difiicult in commercial production is made possible by the substantial elimination of variations, first by the welding of the cone support to the yoke, and secondly by securing the spider 39 to this accurately positioned cone support. The light weight of the movable parts and the strength of the flux in the voice gap result in an unusual volume and fidelity of reproduction. At the same time the extreme simplicity of the structure results in lower cost of production. Thus, the two general objects of the invention are both accomplished at the same time.

Although I have described and illustrated my invention in its preferred embodiments, it is understood that I am not limited thereby, but limit my. invention only by the scope of the appended claims.

I claim: 1

l. The method of producing a field magnet for a loud speaker which consists of piercing a hole in one end of a single bar of metal, shaping said bar to provide a one-piece U-shaped outer pole piece with said hole in one leg thereof, piercing a hole in the other leg axially aligned with the hole in the first leg, line-reaming the two holes, inserting a field coil between the legs of the pole piece, inserting one end of a complete permanently rigid one-piece core through one hole in 5 the outer pole piece and through the field coil, applying a ring gauge between said core and said hole, and permanently securing said end of the core in the other hole of the outer pole piece with a force-fit by driving it therein with the 10 ring gauge centering said core during thepressing operation to position the core irrespective of the parallelism of the legs of the outer pole piece to which the core is secured.

2. The method of attaching a complete per- 15 manently rigid core to a bent-to -shape outer pole piece of a dynamic speaker with said pole piece having outer and inner face portions substantially parallel over their length, which method comprises forming alined voice coil and at- 20 tachment openings in the face portions of said pole piece, the attachment opening being smaller in diameter than an end of said core for the outer pole piece, passing said end of said core through said voice coil open'ng, centering said core in 25 said voice coil opening with a ring gauge, and while maintaining it centered driving its said end into the attachment opening thereby placing said core in a state of elastic compression in said opening and positioning it in said centered 30 position independently of any inaccuracies in the shape of the outer pole piece to which the core is secured.

3. The method of producing the outer polepiece of a field magnet for a loud speaker and 35 attaching sa d pole-piece to a diaphragm supporting frame for said speaker, which method comprises forming a pole-piece to have a pair of substantially parallel face portions, positioning said pole-piece at the rear of said diaphragm 40 frame'and alining said pole piece with relation to said frame, and welding one face portion of said pole-piece at the rear of the frame with the two face portions substantially parallel to the plane of the face of the diaphragm supporting 45 frame, and with said welded fastening such as to make possible an original alinement of said pole piece and frame and then maintain the same in permanent alignment.

4. The method of producing a field magnet 50 for a loud speaker which consists of punching an opening in one portion of a single bar of metal, shaping said bar to provide a one-piece outer pole-piece having a pair of substantially parallel sides with said opening in one side there- 55 of, providing an opening in the other side axially aligned w th the opening in the first side, inserting a field coil between the sides, providing a complete permanently rigid core for said magnet, inserting one end of the core through one 50 opening in the pole-piece and through the field coil, centering said core in said opening with a ring gauge and permanently securing the end of said core in the other opening of the outer pole-piece with a force-fit by driving it therein 55 with the rIng gauge centering said core during the driving operation to position the core irrespective of the parallelism of the sides of the pole-piece to which it is secured.

5. The method of producing a field magnet for 7 a loud speaker which consists in providing al'gned openings in two opposite face portions in an outer pole-piece, line reaming one of said openings with respect to the other opening, inserting a field coil between said face portions of centering means centering said core during the driving operation to position the core irrespective of the parallelism of the face portion of the outer pole-piece to which it is secured.

8. The method of producing a field magnet for a loud speaker which consists of punching a hole in one end of a single bar of metal, thereafter shaping said bar by stamping to provide a onepiece U-shaped pole-piece with said hole in one leg thereof, punching a second hole in the other leg axially aligned with the hole in the first leg,

line-reaming the second hole with respect to the first hole, inserting a field coil between the legs of the pole-piece, inserting one end of a complete permanently rigid core through one hole in the pole-piece and through the field coil, centering said core in said hole by means of a ring gauge, and permanently securing said end of the core in the other hole of the pole-piece with a force-fit by pressing it therein with the ring gauge centering said core during the pressing operation to position the core irrespective of the parallelism of the legs of the pole piece to which it is secured.

'1. The method of attaching a core to a pressedto-shape outer pole-piece of a field magnet of a dynamic speaker with said pole-piece having outer and inner face portions substantially parallel over their length, and store therefor consisting of a one-piece round post, which method comprises providing aligned voice coil and attachment openings in the face portions, the attachment opening being smaller in diameter than an end of the core, inserting a field coil between the face portions, passing said end of the core through said voice coil opening and through said coil, centering said core in said voice coil opening with a ring gauge, and while maintaining it cintered driving its said end into the attachment opening thereby placing said core in a state of elastic compression in said opening and positioning it in said centered'position independ-v ently of any inaccuracies in the shape of the outer pole-piece to which the core is secured,

8. The method of producing a dynamic speaker which includes providing a frustum-like diaphragm supporting frame having attaching portions at the rear thereof, forming an outer pole-piece to have a pair of substantially parallel face portions, providing an opening in one face portion aligned with an opening in the other face portion, positioning said pole-piece with respect to said diaphragm frame at the rear thereof, and welding one face portion at the rear of the frame to provide a permanent alinement of the polepiece with respect to the frame identical with the original positioning, inserting a field coil between the face portions, inserting one end of a core for said pole-piece through one opening and through the field coil to the other opening, centering said core in said one opening with a ring gauge, and while maintaining it centered, driving its end into said other opening to per-- manently maintain said core in said pole-piece, removing said ring gauge and applying a diaphragm with .1 attached voice coil to said diapiece.

aoaasia o eningb meansoraringaau edriv s is' end into the attachment opening, mounting said field magnet on said frame, and mounting a diaphragm on said frame having a voice coil thereon for positioning in said voice coil opening.

10. The method of producing a dynamic speaker, which includes providing a diaphragm supporting frame with a plurality of attaching portions, providing a pressed-to-shape outer polepiece for a field magnet with said outer polepiece including a pair of substantially parallel u sideaand an opening in each side with one opening substantially aligned with the other opening, securing said pole-piece to the attaching portions of said frame at one side of said pole-piece in a permanent and irremovable fastening independently of any securing formations on the joined members, positioning a field coil in said poleinserting a one-piece core through an opening in one side of the pole-piece, and through said field-coil to the opening in the u other side, centering said core in said first opening by means of a ring gauge and while-maintaining it centered, pressing said core into said second opening to be retained therein, and mounting a diaphragm and diaphragm driving 40 means on said frame.

11. The method of producing a dynamic speaker which includes forming a one-piece diaphragm supporting frame from a sheet of metal to have a rimmed face and' attaching portions at the rear, providing a pressed-to-shape outer pole piece for a field magnet with said oute polepiece including a pair of substantially parallel face portions with a voice coil opening in one face portion and a core attachment opening in o the other face portion, with said openings substantially alined with one another, positioning said face portion of the pole-piece having the voice coil opening therein at the attaching portions of the frame and in alinement with the frame such as to make possible subsequent centering of the voice coil in the' voice coil opening, mounting .said face portion at the attaching portions in a permanent fastening such as to preserve said original alinement and mainw tain the same permanently, positioning a field coil in said pole piece, inserting a one-piece core through the voice coil opening, and through said field coil to the attachment opening, centering said core in said voice coil opening with centering .5 means, and while maintaining said core centered, pressing it into said attachment opening to maintain it therein under elastic compression between the core and edges of the attachment opening, and mounting a diaphragm and voice coil on saiddiaphragm frame with said voice coil positioned in said voice coil opening.

12. The method of producing a dynamic speak' l with the p agm frame and outer polepiece as a unit, completing the field magnet struc- II ture and then mounting the diaphragm and voice coil on the diaphragm frame, which method comprises providing a. frustum-like diaphragm supporting frame, shaping a metal bar to have a. pair of substantially parallel face portions, providing an opening in one face portion alined with an opening in the other face portion, alining the pole piece at the rear of the diaphragm frame with respect to said frame, and while alined,

spot welding the pole-piece to the frame in a. unit in permanent alinementgand thereafter completing the field magnet for said speaker by inserting a field coil between the face portions of the outer pole-piece of the unit, inserting one end of a core for said outer pole-piece through one opening and through the field coil to the other opening, centering said core in said one opening with a ring gauge, and while maintaining it centered, driving its end into said other opening to permanently maintain said core in said pole-piece, removing said ring gauge an mounting a diaphragm and a connected voice coil on 10 

